The present invention relates to magnetic recording media, such as thin film magnetic disks, having a polymerized lubricant topcoat thereon. The present invention has particular applicability in manufacturing magnetic recording media suitable for high density recording and long term magnetic performance stability.
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up, flying and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as a xe2x80x9chead crash.xe2x80x9d Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as xe2x80x9ctexturing.xe2x80x9d Conventional texturing techniques include laser texturing the surface of a non-magnetic substrate to provide a textured landing zone in which a magnetic head can land when the drive is not in use, and can take off when the drive is reading and writing data. Typically, the surface of the non-magnetic substrate is polished to a specular finish prior to a laser texturing process to form a landing zone leaving a substantially smooth data zone. Subsequently, an underlayer, a magnetic layer, a protective overcoat and a lubricant topcoat are sequentially deposited, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers. Typical substrate materials include an aluminum alloy with a layer of amorphous nickel phosphorous thereon, glasses, ceramics and glass-ceramic materials, as well as graphite. Underlayers typically comprise chromium or a chromium alloy, while the magnetic layer typically comprises a cobalt based alloy. Protective overcoats typically contain carbon. Such layers are typically deposited by sputtering techniques preformed in an apparatus containing sequential deposition chambers.
The application of the protective layer and the topical lubricant are essential for high durability and reliability of thin film recording media. In accordance with conventional practices, a lubricant topcoat is applied over the protective layer to prevent wear between the disk and head interface during drive operation.
Fluoropolyether lubricants are of particular interest in lubricating magnetic recording media. These lubricants are uniquely suited to form lubricant topcoats on magnetic media because of such properties as chemical inertness, low vapor pressure, low surface tension, high thermal stability, stability under high shear stress and good boundary lubrication properties. Among the many lubricants available, liquid perfluoropolyethers (PFPE) are the most typically used in forming topcoat lubricants on magnetic recording media.
Liquid lubrication of the disk surface encounters several problems, however, which limit its effectiveness as used in rotating storage media. For example, it is well known that non-bonded lubricants will spin off a thin film disk with a carbon overcoat. Typically, PFPE lubricants do not have a retention means so that when the disk rotates, the lubricant tends to spins off the disk. The depletion of the lubricant from the disk surface increases the friction between the disk and the read/write head.
Further, the depletion of the lubricant results in non-uniformity across the surface of the disk resulting in additional operational difficulties. For example, where the thickness is too thin, the head can cause wear on the disk surface and where the lubricant thickness is too great, the head will become stuck in the lubricant (from static friction) and the head or disk could be damaged when the head suddenly becomes unstuck due to the rotating disk.
Burguette et al. in U.S. Pat. No. 4,404,247 disclose anchoring a polymerizable composition directly to a metallized substrate by a complex system which includes an inner polymeric film and an outer polymeric film. The inner polymer is made from a film forming aromatic or heterocyclic polymerizable monomer and a vinyl aromatic polymer and the outer polymer contains a compound having a perfluoropolyether segment. Burguette et al disclose that such a system would adequately protect a metallic thin film and teach away from the use of a hard protective coating on magnetic thin film media. Several other patents to Burguette et al., such as U.S. Pat. Nos. 4,526,833; 4,569,962; 4,671,999; and 4,705,699, disclose additional ingredients in creating the complex two phase polymer coating system.
Accordingly, a continuing need exists in the art for an improved lubricated magnetic recording medium. In particular there exists a need for an efficient, cost-effective method of manufacturing a magnetic recording medium with a lubricant topcoat exhibiting improved tribological performance and fly-stiction.
An advantage of the present invention is an efficient cost-effective method of manufacturing a magnetic recording medium having a lubricant topcoat optimized for tribological performance with reduced fly-stiction.
An additional advantage of the present invention is a magnetic recording medium having an elastomeric lubricant topcoat thereon with improved tribological performance.
Additional advantages and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other aspects are achieved in part by a method of manufacturing a magnetic recording medium with an elastomeric topcoat lubricant. The method comprises forming a protective overcoat on a magnetic layer; applying a fluoropolyether having at least one polymerizable group thereon to the protective overcoat; and polymerizing the fluoropolyether to form an elastomeric topcoat lubricant directly on the protective overcoat.
In embodiments of the present invention, the fluoropolyether, e.g. a perfluoropolyalkylether having more than one acrylate groups, can be polymerized to a crosslinked elastomeric fluoropolyether directly on the protective overcoat with improved tribology. In accordance with embodiments of the present invention, a protective overcoat, e.g. a carbon containing overcoat, can be formed to a thickness of no greater than about 50 xc3x85, e.g. no greater than about 25 xc3x85, with the elastomeric fluoropolyether lubricant topcoat directly on the protective overcoat. The elastomeric topcoat of the present invention advantageously permits a thinner protective overcoat thereby minimizing the fly height of the transducer head over the magnetic recording medium consistent with the demands for higher areal recording density.
Another aspect of the present invention is a magnetic recording medium comprising a protective overcoat and an elastomeric fluoropolyether topcoat directly on the protective overcoat. In an embodiment of the present invention, the magnetic recording medium comprises a substrate; a magnetic layer on the substrate; the protective overcoat on the magnetic layer, e.g. an amorphous carbon layer having a thickness of no greater than about 25 xc3x85; and the elastomeric fluoropolyether topcoat lubricant directly on the protective overcoat.
The inventive magnetic recording medium advantageously comprises a protective overcoat and an elastomeric fluoropolyether topcoat with improved tribological performance at a combined thickness of no greater than about 60 xc3x85. The advantageously thin protective overcoat and lubricant topcoat minimizes the distance between the magnetic layer and the transducer head improving signal and recording performance of the inventive magnetic media when incorporated in a magnetic recording device.
Additional advantages of the present invention will become readily apparent to those having ordinary skill in the art from the following detailed description, wherein the embodiments of the invention are described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.